1. Field of the Invention
The present invention relates generally to a semiconductor device. More specifically, the invention relates to a semiconductor device having a thin film resistor.
2. Description of the Related Art
A passive element for load resistance and bias resistance is formed in addition to an active element, such as a transistor and so forth in a certain type of semiconductor devices. As a resistor to be employed in such semiconductor device, a diffused resistor, a polycrystalline silicon resistor and a metal thin film resistor and so forth are known. Among these, thin film resistor is often employed in applications requiring high reliability, for capability of forming in high precision, lesser secular variation and other excellent properties.
FIG. 1 is a section of the conventional semiconductor device having a thin film resistor. As shown, on the semiconductor substrate 31 formed with predetermined elements, a first interlayer insulation layer 32 of a silicon oxide later or so forth is formed. On the first interlayer insulation layer 32, a thin film resistor 33 of a tungsten silicide (WSi) and so forth and a metal wiring 34 extending the thin film resistor 33 are formed. Furthermore, on the thin film resistor 33 and the metal wiring 34, a second interlayer insulation layer 35 of a silicon oxide layer and so forth is formed.
In the conventional semiconductor device as set forth above, the thin film resistor 33 is entirely enclosed by the interlayer insulation layers 32 and 35. The interlayer insulation layer is required to have a thickness greater than or equal to a given thickness in order to achieve interlayer insulation and to reduce parasitic capacity. Therefore, the insulation layer formed with the silicon oxide layer or so forth have quite low thermal conductivity. For instance, the thermal conductivity of the insulation layer is several digit lesser than that of the metal. Therefore, the thin film resistor has a large thermal resistance to significantly elevate the temperature of the resistor body. This results in variation of the resistance value, peeling off of the insulation layer and variation of characteristics of the active element (e.g. lowering of gm of the transistor) and so forth. Also, elevated temperature of the resistor body may accelerate fatigue of the resistor element in a long period of use.